To capture an image of an object using a camera, an image beam is directed through a lens and onto an image forming medium disposed at an image plane. In conventional photography, photographic film is disposed at the image plane and the image of the object is captured on photographic film. In electronic photography, an imager or image sensor (e.g., a Charge Coupled Device (CCD)), is disposed at the image plane, and the image of the object is captured electronically. For both conventional and electronic photography, it is necessary to properly position the image plane and the lens relative to each other within the camera to provide a focused image.
To properly position the image plane, the position of the image plane needs to be determined. Such a position can be determined relative to a reference surface or reference plane on the camera.
U.S. Pat. Nos. 5,757,485 (Marcus et al) and 5,757,486 (Marcus et al), commonly assigned and incorporated herein by reference, relate to a digital camera image sensor positioning apparatus and method which includes a non-coherent light interferometer. The apparatus and method include an optical probe assembly removably mountable to a digital camera. The non-coherent light interferometer is in communication with the optical probe assembly to determine a depth from a reference surface to the image surface and optical probe assembly. The apparatus and method have been suitable for their intended purpose, however, a need continues to exist for a method for determining (e.g., measuring) a physical distance in a camera between two reference surfaces. Such a method should be robust, comprise simple assembly, be readily constructed and aligned, and usable in a manufacturing environment, particularly by novice users. In particular, for SLR cameras configured for use with 35 mm photographic film or APS format film, a need continues to exist for rapidly measuring a distance between a lens mounting member of the camera and film rails disposed at the image plane. Such a measurement assists in the determination of whether the SLR camera is within manufacturing specifications.